This invention relates to oxygen gas sensors.
Oxygen gas sensors are utilized in such diverse areas as auto-exhaust sensors, sensors in combustion furnaces, steel and glass making, and combustible gas detectors. In the automobile application, oxygen gas sensors continuously monitor exhaust gas oxygen partial pressure which information is used in a feedback manner to adjust the fuel injection system. Known modulating resistive-type oxygen sensors exhibit an electrical conductivity dependence on P.sub.O0.2 given by the formula: .sigma.=constant P.sub.O0.2.sup..+-.1/x in which the factor x typically ranges between 4 and 6. Examples of known ceramics for such applications include Co.sub.1-x Mg.sub.x O and TiO.sub.2. This is a relatively weak dependence. Heretofore, high sensitivity of the oxygen sensor was not required, however, because oxygen partial pressure changed many orders of magnitude around the stoichiometric air fuel ratio operating point of conventional engines. In newly developed lean burn engines, however, the changes in oxygen partial pressure to be detected or controlled are small requiring more highly sensitive sensors.